/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.github.ramerf.wind.core.io;

import io.github.ramerf.wind.core.util.PathUtils;
import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;
import java.nio.file.Files;
import java.nio.file.StandardOpenOption;
import javax.annotation.Nullable;

/**
 * Subclass of {@link UrlResource} which assumes file resolution, to the degree of implementing the
 * {@link WritableResource} interface for it. This resource variant also caches resolved {@link
 * File} handles from {@link #getFile()}.
 *
 * <p>This is the class resolved by {@link DefaultResourceLoader} for a "file:..." URL location,
 * allowing a downcast to {@link WritableResource} for it.
 *
 * <p>Alternatively, for direct construction from a {@link java.io.File} handle, consider using
 * {@link FileSystemResource}. For an NIO {@link java.nio.file.Path}, consider using {@link
 * PathResource} instead.
 *
 * @author Juergen Hoeller
 * @since 5.0.2
 */
public class FileUrlResource extends UrlResource implements WritableResource {

  @Nullable private volatile File file;

  /**
   * Create a new {@code FileUrlResource} based on the given URL object.
   *
   * <p>Note that this does not enforce "file" as URL protocol. If a protocol is known to be
   * resolvable to a file,
   *
   * @param url a URL
   * @see PathUtils#isFileURL(URL)
   * @see #getFile()
   */
  public FileUrlResource(URL url) {
    super(url);
  }

  /**
   * Create a new {@code FileUrlResource} based on the given file location, using the URL protocol
   * "file".
   *
   * <p>The given parts will automatically get encoded if necessary.
   *
   * @param location the location (i.e. the file path within that protocol)
   * @throws MalformedURLException if the given URL specification is not valid
   * @see UrlResource#UrlResource(String, String)
   * @see ResourceResolver#URL_PROTOCOL_FILE
   */
  public FileUrlResource(String location) throws MalformedURLException {
    super(ResourceResolver.URL_PROTOCOL_FILE, location);
  }

  @Override
  public File getFile() throws IOException {
    File file = this.file;
    if (file != null) {
      return file;
    }
    file = super.getFile();
    this.file = file;
    return file;
  }

  @Override
  public boolean isWritable() {
    try {
      URL url = getURL();
      if (PathUtils.isFileURL(url)) {
        // Proceed with file system resolution
        File file = getFile();
        return (file.canWrite() && !file.isDirectory());
      } else {
        return true;
      }
    } catch (IOException ex) {
      return false;
    }
  }

  @Override
  public OutputStream getOutputStream() throws IOException {
    return Files.newOutputStream(getFile().toPath());
  }

  @Override
  public WritableByteChannel writableChannel() throws IOException {
    return FileChannel.open(getFile().toPath(), StandardOpenOption.WRITE);
  }

  @Override
  public Resource createRelative(String relativePath) throws MalformedURLException {
    if (relativePath.startsWith("/")) {
      relativePath = relativePath.substring(1);
    }
    return new FileUrlResource(new URL(getURL(), relativePath));
  }
}
